diff --git a/.env.example b/.env.example
index 4ab6ded239..b5613fdfca 100644
--- a/.env.example
+++ b/.env.example
@@ -525,6 +525,8 @@ OPENID_ON_BEHALF_FLOW_FOR_USERINFO_REQUIRED=
 OPENID_ON_BEHALF_FLOW_USERINFO_SCOPE="user.read" # example for Scope Needed for Microsoft Graph API
 # Set to true to use the OpenID Connect end session endpoint for logout
 OPENID_USE_END_SESSION_ENDPOINT=
+# URL to redirect to after OpenID logout (defaults to ${DOMAIN_CLIENT}/login)
+OPENID_POST_LOGOUT_REDIRECT_URI=
 
 #========================#
 # SharePoint Integration #
diff --git a/api/cache/banViolation.js b/api/cache/banViolation.js
index 3a2d9791b4..122355edb1 100644
--- a/api/cache/banViolation.js
+++ b/api/cache/banViolation.js
@@ -47,7 +47,16 @@ const banViolation = async (req, res, errorMessage) => {
   }
 
   await deleteAllUserSessions({ userId: user_id });
+
+  /** Clear OpenID session tokens if present */
+  if (req.session?.openidTokens) {
+    delete req.session.openidTokens;
+  }
+
   res.clearCookie('refreshToken');
+  res.clearCookie('openid_access_token');
+  res.clearCookie('openid_user_id');
+  res.clearCookie('token_provider');
 
   const banLogs = getLogStores(ViolationTypes.BAN);
   const duration = errorMessage.duration || banLogs.opts.ttl;
diff --git a/api/server/controllers/AuthController.js b/api/server/controllers/AuthController.js
index cb4e1a7eea..22e53dcfc9 100644
--- a/api/server/controllers/AuthController.js
+++ b/api/server/controllers/AuthController.js
@@ -66,14 +66,17 @@ const resetPasswordController = async (req, res) => {
 };
 
 const refreshController = async (req, res) => {
-  const refreshToken = req.headers.cookie ? cookies.parse(req.headers.cookie).refreshToken : null;
-  const token_provider = req.headers.cookie
-    ? cookies.parse(req.headers.cookie).token_provider
-    : null;
-  if (!refreshToken) {
-    return res.status(200).send('Refresh token not provided');
-  }
-  if (token_provider === 'openid' && isEnabled(process.env.OPENID_REUSE_TOKENS) === true) {
+  const parsedCookies = req.headers.cookie ? cookies.parse(req.headers.cookie) : {};
+  const token_provider = parsedCookies.token_provider;
+
+  if (token_provider === 'openid' && isEnabled(process.env.OPENID_REUSE_TOKENS)) {
+    /** For OpenID users, read refresh token from session to avoid large cookie issues */
+    const refreshToken = req.session?.openidTokens?.refreshToken || parsedCookies.refreshToken;
+
+    if (!refreshToken) {
+      return res.status(200).send('Refresh token not provided');
+    }
+
     try {
       const openIdConfig = getOpenIdConfig();
       const tokenset = await openIdClient.refreshTokenGrant(openIdConfig, refreshToken);
@@ -110,7 +113,7 @@ const refreshController = async (req, res) => {
         );
       }
 
-      const token = setOpenIDAuthTokens(tokenset, res, user._id.toString(), refreshToken);
+      const token = setOpenIDAuthTokens(tokenset, req, res, user._id.toString(), refreshToken);
 
       user.federatedTokens = {
         access_token: tokenset.access_token,
@@ -125,6 +128,13 @@ const refreshController = async (req, res) => {
       return res.status(403).send('Invalid OpenID refresh token');
     }
   }
+
+  /** For non-OpenID users, read refresh token from cookies */
+  const refreshToken = parsedCookies.refreshToken;
+  if (!refreshToken) {
+    return res.status(200).send('Refresh token not provided');
+  }
+
   try {
     const payload = jwt.verify(refreshToken, process.env.JWT_REFRESH_SECRET);
     const user = await getUserById(payload.id, '-password -__v -totpSecret -backupCodes');
diff --git a/api/server/controllers/auth/LogoutController.js b/api/server/controllers/auth/LogoutController.js
index 02d3d0302d..ec66316285 100644
--- a/api/server/controllers/auth/LogoutController.js
+++ b/api/server/controllers/auth/LogoutController.js
@@ -5,15 +5,28 @@ const { logoutUser } = require('~/server/services/AuthService');
 const { getOpenIdConfig } = require('~/strategies');
 
 const logoutController = async (req, res) => {
-  const refreshToken = req.headers.cookie ? cookies.parse(req.headers.cookie).refreshToken : null;
+  const parsedCookies = req.headers.cookie ? cookies.parse(req.headers.cookie) : {};
+  const isOpenIdUser = req.user?.openidId != null && req.user?.provider === 'openid';
+
+  /** For OpenID users, read refresh token from session; for others, use cookie */
+  let refreshToken;
+  if (isOpenIdUser && req.session?.openidTokens) {
+    refreshToken = req.session.openidTokens.refreshToken;
+    delete req.session.openidTokens;
+  }
+  refreshToken = refreshToken || parsedCookies.refreshToken;
+
   try {
     const logout = await logoutUser(req, refreshToken);
     const { status, message } = logout;
+
     res.clearCookie('refreshToken');
+    res.clearCookie('openid_access_token');
+    res.clearCookie('openid_user_id');
     res.clearCookie('token_provider');
     const response = { message };
     if (
-      req.user.openidId != null &&
+      isOpenIdUser &&
       isEnabled(process.env.OPENID_USE_END_SESSION_ENDPOINT) &&
       process.env.OPENID_ISSUER
     ) {
@@ -27,7 +40,12 @@ const logoutController = async (req, res) => {
           ? openIdConfig.serverMetadata().end_session_endpoint
           : null;
         if (endSessionEndpoint) {
-          response.redirect = endSessionEndpoint;
+          const endSessionUrl = new URL(endSessionEndpoint);
+          /** Redirect back to app's login page after IdP logout */
+          const postLogoutRedirectUri =
+            process.env.OPENID_POST_LOGOUT_REDIRECT_URI || `${process.env.DOMAIN_CLIENT}/login`;
+          endSessionUrl.searchParams.set('post_logout_redirect_uri', postLogoutRedirectUri);
+          response.redirect = endSessionUrl.toString();
         } else {
           logger.warn(
             '[logoutController] end_session_endpoint not found in OpenID issuer metadata. Please verify that the issuer is correct.',
diff --git a/api/server/middleware/validateImageRequest.js b/api/server/middleware/validateImageRequest.js
index b74ed7225e..4d954d07c4 100644
--- a/api/server/middleware/validateImageRequest.js
+++ b/api/server/middleware/validateImageRequest.js
@@ -68,17 +68,11 @@ function createValidateImageRequest(secureImageLinks) {
       }
 
       const parsedCookies = cookies.parse(cookieHeader);
-      const refreshToken = parsedCookies.refreshToken;
-
-      if (!refreshToken) {
-        logger.warn('[validateImageRequest] Token not provided');
-        return res.status(401).send('Unauthorized');
-      }
-
       const tokenProvider = parsedCookies.token_provider;
       let userIdForPath;
 
       if (tokenProvider === 'openid' && isEnabled(process.env.OPENID_REUSE_TOKENS)) {
+        /** For OpenID users with OPENID_REUSE_TOKENS, use openid_user_id cookie */
         const openidUserId = parsedCookies.openid_user_id;
         if (!openidUserId) {
           logger.warn('[validateImageRequest] No OpenID user ID cookie found');
@@ -92,6 +86,17 @@ function createValidateImageRequest(secureImageLinks) {
         }
         userIdForPath = validationResult.userId;
       } else {
+        /**
+         * For non-OpenID users (or OpenID without REUSE_TOKENS), use refreshToken from cookies.
+         * These users authenticate via setAuthTokens() which stores refreshToken in cookies.
+         */
+        const refreshToken = parsedCookies.refreshToken;
+
+        if (!refreshToken) {
+          logger.warn('[validateImageRequest] Token not provided');
+          return res.status(401).send('Unauthorized');
+        }
+
         const validationResult = validateToken(refreshToken);
         if (!validationResult.valid) {
           logger.warn(`[validateImageRequest] ${validationResult.error}`);
diff --git a/api/server/routes/oauth.js b/api/server/routes/oauth.js
index 0b1252f636..64d29210ac 100644
--- a/api/server/routes/oauth.js
+++ b/api/server/routes/oauth.js
@@ -42,7 +42,7 @@ const oauthHandler = async (req, res, next) => {
       isEnabled(process.env.OPENID_REUSE_TOKENS) === true
     ) {
       await syncUserEntraGroupMemberships(req.user, req.user.tokenset.access_token);
-      setOpenIDAuthTokens(req.user.tokenset, res, req.user._id.toString());
+      setOpenIDAuthTokens(req.user.tokenset, req, res, req.user._id.toString());
     } else {
       await setAuthTokens(req.user._id, res);
     }
diff --git a/api/server/services/AuthService.js b/api/server/services/AuthService.js
index 0cb418e076..a400bce8b7 100644
--- a/api/server/services/AuthService.js
+++ b/api/server/services/AuthService.js
@@ -411,14 +411,17 @@ const setAuthTokens = async (userId, res, _session = null) => {
 /**
  * @function setOpenIDAuthTokens
  * Set OpenID Authentication Tokens
- * //type tokenset from openid-client
+ * Stores tokens server-side in express-session to avoid large cookie sizes
+ * that can exceed HTTP/2 header limits (especially for users with many group memberships).
+ *
  * @param {import('openid-client').TokenEndpointResponse & import('openid-client').TokenEndpointResponseHelpers} tokenset
  * - The tokenset object containing access and refresh tokens
+ * @param {Object} req - request object (for session access)
  * @param {Object} res - response object
  * @param {string} [userId] - Optional MongoDB user ID for image path validation
  * @returns {String} - access token
  */
-const setOpenIDAuthTokens = (tokenset, res, userId, existingRefreshToken) => {
+const setOpenIDAuthTokens = (tokenset, req, res, userId, existingRefreshToken) => {
   try {
     if (!tokenset) {
       logger.error('[setOpenIDAuthTokens] No tokenset found in request');
@@ -445,18 +448,30 @@ const setOpenIDAuthTokens = (tokenset, res, userId, existingRefreshToken) => {
       return;
     }
 
-    res.cookie('refreshToken', refreshToken, {
-      expires: expirationDate,
-      httpOnly: true,
-      secure: isProduction,
-      sameSite: 'strict',
-    });
-    res.cookie('openid_access_token', tokenset.access_token, {
-      expires: expirationDate,
-      httpOnly: true,
-      secure: isProduction,
-      sameSite: 'strict',
-    });
+    /** Store tokens server-side in session to avoid large cookies */
+    if (req.session) {
+      req.session.openidTokens = {
+        accessToken: tokenset.access_token,
+        refreshToken: refreshToken,
+        expiresAt: expirationDate.getTime(),
+      };
+    } else {
+      logger.warn('[setOpenIDAuthTokens] No session available, falling back to cookies');
+      res.cookie('refreshToken', refreshToken, {
+        expires: expirationDate,
+        httpOnly: true,
+        secure: isProduction,
+        sameSite: 'strict',
+      });
+      res.cookie('openid_access_token', tokenset.access_token, {
+        expires: expirationDate,
+        httpOnly: true,
+        secure: isProduction,
+        sameSite: 'strict',
+      });
+    }
+
+    /** Small cookie to indicate token provider (required for auth middleware) */
     res.cookie('token_provider', 'openid', {
       expires: expirationDate,
       httpOnly: true,
diff --git a/api/strategies/openIdJwtStrategy.js b/api/strategies/openIdJwtStrategy.js
index 5d9eb14085..df318ca30e 100644
--- a/api/strategies/openIdJwtStrategy.js
+++ b/api/strategies/openIdJwtStrategy.js
@@ -81,10 +81,18 @@ const openIdJwtLogin = (openIdConfig) => {
             await updateUser(user.id, updateData);
           }
 
-          const cookieHeader = req.headers.cookie;
-          const parsedCookies = cookieHeader ? cookies.parse(cookieHeader) : {};
-          const accessToken = parsedCookies.openid_access_token;
-          const refreshToken = parsedCookies.refreshToken;
+          /** Read tokens from session (server-side) to avoid large cookie issues */
+          const sessionTokens = req.session?.openidTokens;
+          let accessToken = sessionTokens?.accessToken;
+          let refreshToken = sessionTokens?.refreshToken;
+
+          /** Fallback to cookies for backward compatibility */
+          if (!accessToken || !refreshToken) {
+            const cookieHeader = req.headers.cookie;
+            const parsedCookies = cookieHeader ? cookies.parse(cookieHeader) : {};
+            accessToken = accessToken || parsedCookies.openid_access_token;
+            refreshToken = refreshToken || parsedCookies.refreshToken;
+          }
 
           user.federatedTokens = {
             access_token: accessToken || rawToken,